Circuit board

ABSTRACT

A circuit board includes a laminated body including a laminate of a plurality of insulating-material layers made of a flexible material. External electrodes are provided on the top surface of the laminated body. An electronic component is mounted on the external electrodes. A plurality of internal conductors, when viewed in plan in the z-axis direction, are overlaid on the external electrodes and are not connected to one another in regions in which the internal conductors are overlaid on the external electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to circuit boards, and more particularly,to a circuit board on which an electronic component is to be mounted.

2. Description of the Related Art

Circuit boards including laminates of ceramic layers are known asconventional general circuit boards. FIG. 10 is a diagram illustrating aconventional circuit board 500 mounted on a printed wiring board 600. Inaddition, an electronic component 700 is mounted on the circuit board500.

As illustrated in FIG. 10, the circuit board 500 is composed of a mainbody 501 and external electrodes 502 and 503. The main body 501 iscomposed of a laminate of ceramic layers and is a rigid board. Theexternal electrodes 502 and 503 are provided on a top surface and abottom surface, respectively, of the main body 501.

The printed wiring board 600 is a motherboard mounted on, for example,an electronic device, such as a mobile phone, and is provided with amain body 601 and external electrodes 602, as illustrated in FIG. 10.The main board is a rigid board made of resin or the like. The externalelectrodes 602 are provided on a top surface of the main body 601.

The electronic component 700 is, for example, a semiconductor integratedcircuit and is provided with a main body 701 and external electrodes702. The main body 701 is a semiconductor board. The external electrodes702 are provided on the bottom surface of the main body 701.

As illustrated in FIG. 10, the circuit board 500 is mounted on theprinted wiring board 600. Specifically, the circuit board 500 is mountedby connecting the external electrodes 502 to the external electrodes 602by solder.

As illustrated in FIG. 10, the electronic component 700 is mounted onthe circuit board 500. Specifically, the electronic component 700 ismounted by connecting the external electrodes 503 to the externalelectrodes 702 by solder. The circuit board 500, the printed wiringboard 600, and the electronic component 700 described above are to bemounted in an electronic device, such as a mobile phone.

Meanwhile, the conventional circuit board 500 has a problem in that itis likely to be detached from the printed wiring board 600. Morespecifically, it is likely that the printed wiring board 600 is bent byshock generated when the electronic component containing the circuitboard 500 and the printed wiring board 600 is dropped. Even if theprinted wiring board 600 is bent, the circuit board 500 may not be bentsignificantly along with the bending of the printed wiring board 600since the circuit board 500 is a rigid board. Thus, stress is imposed onthe solder connecting the external electrodes 502 to the externalelectrodes 602. As a result, the solder is broken, and the circuit board500 is detached from the printed wiring board 600.

To overcome the above problem, the circuit board 500 may be fabricatedby laminating sheets made of a flexible material. A printed circuitboard disclosed in Japanese Unexamined Patent Application PublicationNo. 2006-93438, for example, includes a laminate of sheets made of aflexible material. FIG. 10 is used as a reference of a configuration ofa printed board 800.

The printed board 800 disclosed in Japanese Unexamined PatentApplication Publication No. 2006-93438 includes a main body 801 andexternal electrodes (lands) 802 and 803. The main body 801 is composedof a laminate of sheets made of thermoplastic resin. The externalelectrodes 802 and 803 are provided on the top surface and the bottomsurface, respectively, of the main body 801. Similarly to the circuitboard 500, the printed board 800 is mounted on the printed wiring board600 through the external electrodes 802 on the bottom surface. Similarlyto the circuit board 500, the electronic component 700 is mounted on theprinted board 800 through the external electrodes 803 on the topsurface.

However, in the printed board 800 disclosed in Japanese UnexaminedPatent Application Publication No. 2006-93438, the electronic component700 is likely to be detached. Specifically, the printed board 800 can bebent since it is composed of sheets made of a flexible material. Thus,if the printed wiring board 600 is bent, the printed board 800 can bebent along with the bending of the printed wiring board 600. Thus, it ispossible to prevent the printed board 800 from being detached from theprinted wiring board 600 due to breakage of solder connecting theexternal electrodes 602 and the external electrodes 802.

Meanwhile, the printed board 800 has flexibility over its entiresurface, and thus, the entire surface of the printed board 800 can bebent. On the other hand, the electronic component 700 is composed of asemiconductor board and, thus, cannot be bent significantly. Thus,stress is imposed on the external electrodes 702 and 803 and the solderconnecting the external electrodes 702 and 803. As a result, the soldermay be broken, and the external electrodes 702 and 803 may be detachedfrom the main bodies 701 and 801. That is, the electronic component 700and the printed board 800 may be disconnected.

In FIG. 10, the printed board 800 is attached to the printed wiringboard 600 through the external electrodes 802. However, in a case inwhich the printed board 800 is attached to a casing by an adhesive orother material, the problem of possible disconnection between theelectronic component 700 and the printed board 800 may also occur.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a circuit board which prevents an electroniccomponent from being detached from the circuit board.

A circuit board according to a preferred embodiment of the presentinvention preferably includes a laminated body including a laminate of aplurality of insulating-material layers made of a flexible material, afirst external electrode which is provided on a top surface of thelaminated body and on which an electronic component is to be mounted,and a plurality of internal conductors which, when viewed in plan in alamination direction, are overlaid on the first external electrode andare not connected to one another through via hole conductors in a regionin which the internal conductors are overlaid on the first externalelectrode.

According to various preferred embodiments of the present invention, anelectronic component is prevented from being detached from a circuitboard.

The above and other elements, features, steps, characteristics, andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a circuit board according to apreferred embodiment of the present invention.

FIG. 2 is an exploded perspective view of the circuit board in FIG. 1.

FIG. 3 is a cross-sectional structural view of the circuit board in FIG.1 which is taken along line A-A.

FIG. 4 is a perspective view of the circuit board in FIG. 1 viewed inthe lamination direction.

FIG. 5 is configuration diagram illustrating a module having the circuitboard in FIG. 1.

FIG. 6 is an exploded perspective view of a circuit board according to afirst modified example of a preferred embodiment of the presentinvention.

FIG. 7 is an exploded perspective view of a circuit board according to asecond modified example of a preferred embodiment of the presentinvention.

FIG. 8 is an exploded perspective view of a circuit board according to athird modified example of a preferred embodiment of the presentinvention.

FIG. 9 is an exploded perspective view of a circuit board according to afourth modified example of a preferred embodiment of the presentinvention.

FIG. 10 is a diagram illustrating a conventional circuit board mountedon a printed wiring board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a circuit board according to preferred embodiments ofthe present invention will be described with reference to the drawings.

In the following, a configuration of a circuit board according topreferred embodiments of the present invention will be described withreference to the drawings. FIG. 1 is an external perspective view of acircuit board 10 according to a preferred embodiment of the presentinvention. FIG. 2 is an exploded perspective view of the circuit board10 in FIG. 1. FIG. 3 is a cross-sectional structural view of the circuitboard 10 in FIG. 1 which is taken along line A-A. FIG. 4 is aperspective view from a lamination direction of the circuit board 10 inFIG. 1. In FIGS. 1 to 4, a lamination direction is defined as adirection in which insulating-material layers are laminated duringfabrication of the circuit board 10. The lamination direction isreferred to as a z-axis direction. A direction along the long sides ofthe circuit board 10 is referred to as an x-axis direction, and adirection along the short sides of the circuit board 10 is referred toas a y-axis direction. Further, in the circuit board 10, a surface atthe forward side in the z-axis direction is referred to as a topsurface, a surface at the rearward side in the z-axis direction isreferred to as a bottom surface, and the other sides are referred to asside surfaces.

As illustrated in FIG. 1 and FIG. 2, the circuit board 10 preferablyincludes a laminated body 11, external electrodes 12 a to 12 d and 14 ato 14 f, internal conductors 18 a to 18 d, 20 a to 20 f, and 22 a and 22b, and via hole conductors b1 to b11. As illustrated in FIG. 2, thelaminated body 11 preferably includes a laminate of rectangular orsubstantially rectangular insulating-material layers 16 a to 16 h madeof a flexible material, for example, a thermoplastic resign, such asliquid crystal polymer. Thus, the laminated body 11 has preferably arectangular or substantially rectangular parallelepiped shape.Hereinafter, a front surface of the insulating-material layers 16 refersto a main surface at the forward side in the z-axis direction, and aback surface of the insulating-material layers 16 refers to a mainsurface at the backward side in the z-axis direction.

The external electrodes 12 are preferably layers made of a conductivematerial, for example, copper, and provided on the top surface of thelaminated body 11, as illustrated in FIG. 1. More specifically, theexternal electrodes 12 are provided near the approximate center (theintersection point of diagonals) of the front surface of the insulatinglayer 16 a which is provided at the forward-most side in the z-axisdirection. The external electrodes 12 a and 12 b are arranged along they-axis direction. The external electrodes 12 c and 12 d are arrangedalong the y-axis direction at positions closer to the forward side inthe x-axis direction than positions of external electrodes 12 a and 12b. Moreover, the external electrodes 12 are categorized into two groups(groups G1 and G2). Specifically, the external electrodes 12 a and 12 bbelong to the group G1. The external electrodes 12 c and 12 d belong tothe group G2. The external electrodes 12 are arranged to be connected toan electronic component to be mounted on the top surface of thelaminated body 11.

The internal conductors 18 a to 18 d are preferably a wiring layer madeof a conductive material, for example, copper, and disposed in thelaminated body 11, as illustrated in FIG. 2. Specifically, the internalconductors 18 are provided on the front surface of theinsulating-material layer 16 b. The internal conductors 18 a to 18 d areoverlaid on the external electrodes 12 a to 12 d, respectively, whenviewed in plan in the z-axis direction. In FIG. 2, only portions of theinternal conductors 18 on which the external electrodes 12 a to 12 d areoverlaid are shown, and illustration of the other portions is omitted.

The internal conductors 20 a to 20 f are preferably film-shapedconductors having relatively large areas, such as capacitor conductorsand ground conductors, made of a conductive material, for example,copper, and are provided in the laminated body 11. The internalconductors 20 a to 20 f are provided on a plurality ofinsulating-material layers 16. Specifically, the internal conductors 20a and 20 b are preferably arranged along the x-axis direction on thefront surface of the insulating-material layer 16 c. The internalconductors 20 c and 20 d are preferably arranged along the x-axisdirection on the front surface of the insulating-material layer 16 d.The internal conductors 20 e and 20 f are preferably arranged along thex-axis direction on the front surface of the insulating-material layer16 e.

Further, as illustrated in FIG. 4, the internal conductors 20 a, 20 c,and 20 e are preferably overlaid on one another so as to coincide withone another and also overlaid on the external electrodes 12 a and 12 bthat belong to the group G1 when viewed in plan in the z-axis direction.In this manner, the external electrodes 12 a and 12 b are overlaid on aplurality of internal conductors 20 when viewed in plan in the z-axisdirection. In addition, when viewed in plan in the z-axis direction, theinternal conductors 20 a, 20 c, and 20 e are not connected to oneanother through via hole conductors in the regions where the internalconductors 20 a, 20 c, and 20 e are overlaid on the external electrodes12 a and 12 b.

The internal conductors 20 b, 20 d, and 20 f are preferably overlaid onone another so as to coincide with one another and also overlaid on theexternal electrodes 12 c and 12 d that belong to the group G2 whenviewed in plan in the z-axis direction. In this manner the externalelectrodes 12 c and 12 d are overlaid on a plurality of internalconductors 20 when viewed in plan in the z-axis direction. When viewedin plan in the z-axis direction, the internal conductors 20 b, 20 d, and20 f are not connected to one another through via hole conductors in theregions in which the internal conductors 20 b, 20 d, and 20 f areoverlaid on the external electrodes.

The internal conductors 22 are preferably wiring layers made of aconductive material, for example, copper, and provided in the laminatedbody 11, as illustrated in FIG. 2. Specifically, the internal conductors22 a and 22 b are provided on the front surfaces of theinsulating-material layers 16 f and 16 g, respectively. In FIG. 2, onlyportions around end portions of the internal conductors 22 are shown,and illustration of the other portions are omitted.

The external electrodes 14 preferably include a layer made of aconductive material, for example, copper, and provided on the bottomsurface of the laminated body 11. That is, the external electrodes 14are provided on the back surface of the insulating-material layer 16 hthat is provided at the backward-most side in the z-axis direction.Further, the external electrodes 14 a to 14 c are arranged along theshort side at the backward side in the x-axis direction on the bottomsurface of the laminated body 11. The external electrodes 14 d to 14 fare arranged along the short side at the forward side in the x-axisdirection on the bottom surface of the laminated body 11. In thismanner, the external electrodes 12 and the external electrodes 14 arenot overlaid on each other when viewed in plan view in the z-axisdirection, as illustrated in FIG. 4. The external electrodes 14 arearranged to be connected to a printed wiring board to be mounted on thebottom surface of the laminated body 11.

As illustrated in FIG. 3, the laminated body 11 preferably includes acoil (circuit element) L and a capacitor (circuit element) C. The coil Lis preferably defined by internal conductors (omitted in FIG. 2) and viahole conductors (not shown) which are provided on the front surfaces ofthe insulating-material layers 16 d to 16 g. The capacitor C ispreferably defined by internal conductors (omitted in FIG. 2) providedon the front surfaces of the insulating-material layers 16 f and 16 g.As illustrated in FIG. 3, the internal conductors 20 a, 20 c, and 20 eand the internal conductors 20 b, 20 d, and 20 f are provided atpositions upward from the center surface with respect to the z-axisdirection.

The via hole conductors b1 to b11 connect the external electrodes 12 and14, the internal conductors 18, 20, and 22, and the coil L and thecapacitor C and are disposed so as to penetrate the insulating-materiallayers 16 in the z-axis direction. Specifically, as illustrated in FIG.2, the via hole conductors b1 to b4 penetrate the insulating-materiallayer 16 a in the z-axis direction to connect the external electrodes 12a to 12 d to the internal conductors 18 a to 18 d, respectively.

The via hole conductor b5 penetrates the insulating-material layer 16 fin the z-axis direction and is not overlaid on the external electrodes12 when viewed in plan in the z-axis direction, as illustrated in FIG.2. The via hole conductor b5 connects the internal conductor 22 a to theinternal conductor 22 b. While FIG. 2 shows only the via hole conductorb5 as a via hole connecting the internal conductors 22 to each other, avia hole conductor other than the via hole conductor b5 to connect theinternal conductors 22 to each other may also be present. However, anyvia hole conductor that connects the internal conductors 22 to eachother is preferably not overlaid on the external electrodes 12.

As illustrated in FIG. 2, the via hole conductors b6 to b11 penetratethe insulating-material layer 16 h in the z-axis direction and are notoverlaid on the external electrodes 12 when viewed in plan in the z-axisdirection. The via hole conductors b6 to b11 connect the internalconductors 22 provided on the insulating-material layers 16 f and 16 gto the external electrodes 14 a to 14 f, respectively.

By laminating the insulating-material layers 16 a to 16 h configured asdescribed above, the circuit board 10 illustrated in FIG. 1 is obtained.

FIG. 5 is a diagram illustrating a configuration of a module 150including the circuit board 10. The module 150 preferably includes thecircuit board 10, an electronic component 50, and a printed wiring board100.

As illustrated in FIG. 5, the electronic component 50 is preferably adevice, such as a semiconductor integrated circuit, for example, mountedon the circuit board 10. The electronic component 50 includes a mainbody 52 and external electrodes 54 a to 54 d. The main body 52 ispreferably a rigid board defined by, for example, a semiconductorsubstrate. The external electrodes 54 are provided on a main surface atthe rearward side in the z-axis direction (bottom surface) of the mainbody 52. The external electrodes 54 a to 54 d are preferably connectedto the external electrodes 12 a to 12 d, respectively, by solder 60, forexample. In this manner, the electronic component 50 is mounted on thetop surface of the circuit board 10.

The printed wiring board 100 preferably includes a main body 102 andexternal electrodes 104 a to 104 f. The main body 102 is preferably arigid board made of resin, for example. The external electrodes 104 areprovided on a main surface at the forward side in the z-axis direction(top surface) of the main body 102. The external electrodes 104 a to 104f are connected to the external electrodes 14 a to 14 f, respectively,preferably by a bonding agent, such as solder 70. In this manner, thecircuit board 10 is mounted on the printed wiring board 100 via thebottom surface. The module 150 described above is mounted on anelectronic device such as a mobile phone.

In the following, a manufacturing method of the circuit board 10 will bedescribed with reference to the drawings. First, the insulating-materiallayers 16 each of which including copper foil formed over the entiretyor substantially the entirety of one of the main surfaces are prepared.In each of the insulating-material layers 16 a to 16 g, the main surfaceon which the copper foil is formed is herein referred to as the frontsurface. On the other hand, in the insulating-material layer 16 h, themain surface on which the copper foil is formed is herein referred to asthe back surface.

Then, the positions at which the via hole conductors b1 to b5 of theinsulating-material layers 16 a and 16 f are to be formed (see, FIG. 2)are irradiated with laser beams from the back surfaces, so that the viaholes are formed. The positions at which the via hole conductor b6 tob11 of the insulating-material layer 16 h are to be formed (see, FIG. 2)are irradiated with laser beams from the front surface, so that the viaholes are formed. In addition, via holes may also be formed in theinsulating-material layers 16 b to 16 e and 16 g as necessary.

In the following, the external electrodes 12 illustrated in FIG. 2 arepreferably formed on the front surface of the insulating-material layer16 a by photolithographic processes, for example. Specifically, resistshaving the same shapes as the external electrodes 12 illustrated in FIG.2 are printed on the copper foil of the insulating-material layer 16 a.Then, the copper foil is etched so that the copper foil on the portionwhich is not covered by the resists is removed. Then, the resist isremoved. In this manner, the external electrodes 12 illustrated in FIG.2 are formed on the front surface of the insulating-material layer 16 a.

Then, the internal conductors 18 illustrated in FIG. 2 are preferablyformed on the front surface of the insulating-material layer 16 b byphotolithographic processes. The internal conductors 20 illustrated inFIG. 2 are formed on the front surfaces of the insulating-materiallayers 16 c to 16 e by photolithographic processes, for example. Theinternal conductors 22 illustrated in FIG. 2 are formed on the frontsurfaces of the insulating-material layers 16 f and 16 g byphotolithographic processes. The internal electrodes defining the coil Land the capacitor C illustrated in FIG. 3 (not shown in FIG. 2) arepreferably formed on the front surfaces of the insulating-materiallayers 16 d to 16 g by photolithographic processes, for example. Theexternal electrodes 14 illustrated in FIG. 2 are preferably formed onthe back surface of the insulating-material layer 16 h byphotolithographic processes, for example. These photolithographicprocesses are similar to the photolithographic processes used when theexternal electrodes 12 are formed, and the description thereof will beomitted.

Then, the via holes formed in the insulating-material layers 16 a, 16 f,and 16 h are filled with conductive paste preferably made primarily ofcopper, for example, so that the via hole conductors b1 to b11 areformed. If the via holes have been formed on the insulating-materiallayers 16 b to 16 e and 16 g, these via holes are also filled withconductive paste.

Then, the insulating-material layers 16 a to 16 h are laminated in thatorder. By applying force to the insulating-material layers 16 a to 16 hfrom opposite directions in the lamination direction, theinsulating-material layers 16 a to 16 h are press-bonded. In thismanner, the circuit board 10 illustrated in FIG. 1 is obtained.

As will be described below, in the circuit board 10, even if the shapeof the printed wiring board 100 is changed, the circuit board 10 can beprevented from being detached from the printed wiring board 100. Morespecifically, bending of the printed wiring board 600 may occur due toshock caused by dropping of an electronic device in which theconventional circuit board 500 and printed wiring board 600 are mounted.Since the circuit board 500 is a rigid board, in the case of bending ofthe printed wiring board 600, the shape of the circuit board 500 may notbe significantly changed in accordance with the bending of the printedwiring board 600. Therefore, pressure is imposed on the solderconnecting the external electrodes 502 and the external electrodes 602.As a result, the solder may be broken, and the circuit board 500 may bedetached from the printed wiring board 600.

Thus, in the circuit board 10, the laminated body 11 preferably includesa laminate of insulating-material layers 16 made of a flexible material.Therefore, the circuit board 10 can be bent more easily than the circuitboard 500. Therefore, even when the printed wiring board 100 is bent andthe interval between the external electrodes 104 are changed due todropping of an electronic device in which the module 150 illustrated inFIG. 5 is mounted, the intervals of the external electrodes 14 can alsobe changed by the deformation of the circuit board 10. As a result,pressure on the solder connecting the external electrodes 14 and theexternal electrodes 104 is effectively reduced or prevented, whichprevents the circuit board 10 from being detached from the printedwiring board 100.

Further, in the circuit board 10, the electronic component 50 isprevented from being detached from the circuit board 10, as will bedescribed below. More specifically, since the printed wiring board 800disclosed in Japanese Unexamined Patent Application Publication No.2006-93438 illustrated in FIG. 10 has flexibility over its entiresurface, the entire printed wiring board 800 may be bent. Thus, theintervals between the external electrodes 803 may be changed. On theother hand, since the electronic component 700 includes a semiconductorsubstrate, the electronic component 803 cannot be significantly bent.Therefore, pressure is imposed on the external electrodes 702 and 803and the solder connecting therebetween. As a result, the solder may bebroken and the external electrodes 702 and 803 may be detached from themain bodies 701 and 801. That is, the electronic component 700 and theprinted wiring board 800 may be disconnected.

Accordingly, the circuit board 10 effectively prevents the electroniccomponent 50 from being detached from the circuit board 10 by overlayingat least one of the internal conductors 18, 20, and 22 on the externalelectrodes 12 when viewed in plan in the z-axis direction. Morespecifically, when the printed wiring board 100 is bent in a convexmanner, stresses are applied to the external electrodes 104 indirections indicated by arrows B, as illustrated in FIG. 5. The externalelectrodes 104 are connected to the external electrodes 14 via thesolder 70. Further, the laminated body 11 has flexibility. Therefore,the external electrodes 14 receive stresses in the directions indicatedby the arrows B in accordance with the displacement of the externalelectrodes 104. As a result, tensile stresses α1 are applied to theinsulating-material layers 16 e to 16 h in the x-axis direction.

Note that the internal conductors 20 are preferably fabricated usingmetal foil, such as copper, for example, and the insulating-materiallayers 16 are preferably fabricated using thermoplastic resin, such asliquid crystal polymer, for example. Since the insulating-materiallayers 16 and the internal conductors 20 are simply press-bondedtogether, no chemical bonding is formed between the insulating-materiallayers 16 and the internal conductors 20. Thus, the insulating-materiallayers 16 and the internal conductors 20 can be displaced with respectto each other. Therefore, when the tensile stresses are generated in theinsulating-material layers 16 e to 16 h, the insulating-material layer16 d is displaced with respect to the internal conductors 20 e and 20 f.Similarly, the insulating-material layer 16 c is displaced with respectto the internal conductors 20 c and 20 d. Similarly, theinsulating-material layer 16 b is displaced with respect to the internalconductors 20 a and 20 b.

As described above, when displacement between the insulating-materiallayers 16 and the internal conductors 20 occurs, a force is nottransmitted from the insulating-material layers 16 provided at thebackward side in the z-axis direction to the insulating-material layers16 provided at the forward side in the z-axis direction. Thus, tensilestresses α2 to α4 generated in the insulating-material layers 16 d, 16c, and 16 b are less than the tensile stresses α1 generated in theinsulating-material layers 16 e to 16 h. More specifically, themagnitudes of the tensile stresses α1 to α4 progressively decrease inthat order. Therefore, the tension in the x-axis direction generated inthe insulating-material layers 16 a to 16 h progressively decreases inorder from the backward side to the forward side in the z-axisdirection. Accordingly, the external electrodes 12 a and 12 b providedon the front surface of the insulating-material layer 16 a are notsignificantly displaced. As a result, the circuit board 10 prevents theelectronic component 50 from being detached from the circuit board 10.In addition, even when one of the main surfaces of an internal conductorand one of the main surfaces of an insulating-material layer is stronglybonded together by, for example, anchor effect, as in the case betweenthe insulating-material layer 16 d and the internal conductor 20 e andbetween the insulating-material layer 16 c and the internal conductor 20c, it is possible to cause displacement in the other main surface of theinternal conductor to relax the stresses α if internal conductors arepresent on multiple layers.

In particular, in the circuit board 10, a plurality of internalconductors 20 are overlaid on the external electrodes when viewed inplan in the z-axis direction. Thus, the tensile stresses generated inthe insulating-material layers 16 are more effectively relaxed. As aresult, the electronic component 50 is more effectively prevented frombeing detached from the circuit board 10.

Further, in the circuit board 10, when shock is applied on the printedwiring board 100 from the rearward side towards the forward side in thez-axis direction, the shock is prevented from being transmitted to theexternal electrodes 12. More specifically, the via hole conductors aremore rigid than the insulating-material layers 16 since the via holeconductors are made of a conductive material. Therefore, when the viahole conductors connecting the internal conductors 18, 20, and 22 areoverlaid on the external electrodes 12 when viewed in plan in the z-axisdirection, the shock may be transmitted from the external electrodes 12through the via hole conductors.

Accordingly, in the circuit board 10, the via hole conductor b5connecting the internal conductors 22 to each other is preferably notoverlaid on the external electrodes 12 when viewed in plan in the z-axisdirection, and the internal conductors 20 are not connected to oneanother in the region in which the internal conductors 20 are overlaidon the external electrodes 12, when viewed in plan in the z-axisdirection. That is, the external electrodes 12, when viewed in plan inthe z-axis direction, are preferably not overlaid on the via holeconductors other than the via hole conductors b1 to b4. Therefore, whenshock is applied to the printed wiring board 100, the shock is nottransmitted to the external electrodes 12 through the via holeconductors. As a result, when shock is applied to the printed wiringboard 100 from the rearward side towards the forward side in the z-axisdirection, the shock is prevented from being transmitted to the externalelectrodes 12.

Further, in the circuit board 10, when shock is applied to the printedwiring board 100 from the rearward side towards the forward side in thez-axis direction, the shock is prevented from being transmitted to theexternal electrodes 12 also for the reason described below. Morespecifically, shock from the printed wiring board 100 is transmitted tothe laminated body 11 through the external electrodes 104, the solder70, and the external electrodes 14. Thus, it is preferable that theexternal electrodes 12 be disposed as far as possible from the externalelectrodes 14. Accordingly, in the circuit board 10, the externalelectrodes 12 are disposed so as not to be overlaid on the externalelectrodes 14 when viewed in plan in the z-axis direction. In thismanner, when shock is applied to the printed wiring board 100 from therearward side towards the forward side in the z-axis direction, theshock is prevented from being transmitted to the external electrodes 12.To achieve the effects described above, it is preferable that theinternal conductors be disposed as close as possible to the externalelectrodes 12.

In the following, a circuit board 10 a according to a first modifiedexample of a preferred embodiment of the present invention will bedescribed with reference to the drawing. FIG. 6 is an explodedperspective view of the circuit board 10 a according to the firstmodified example.

The circuit board 10 a is different from the circuit board 10 in that itpreferably includes internal conductors (auxiliary conductors) 24 a to24 c. More specifically, the internal conductor 24 a is preferablyprovided on the front surface of the insulating-material layer 16 cprovided with the internal conductors 20 a and 20 b, along the directionin which the internal conductors 20 a and 20 b are arranged, i.e., thex-axis direction. Similarly, the internal conductor 24 b is preferablyprovided on the front surface of the insulating-material layer 16 dprovided with the internal conductors 20 c and 20 d, along the directionin which the internal conductors 20 c and 20 d are arranged, i.e.,x-axis direction. Similarly, the internal conductor 24 c is preferablyprovided on the front surface of the insulating-material layer 16 eprovided with the internal conductors 20 e and 20 f, along the directionin which the internal conductors 20 e and 20 f are arranged, i.e.,x-axis direction.

The internal conductors 24 provided as described above make it difficultfor the insulating-material layers 16 to be stretched in the directionin which the internal conductors 20 are arranged (x-axis direction). Asa result, even if the shape of the printed wiring board 100 is changed,the external electrodes 12 a and 12 b provided on the front surface ofthe insulating-material layer 16 a are not significantly displaced. As aresult, the circuit board 10 a more effectively prevents the electroniccomponent 50 from being detached from the circuit board 10 a.

In the following, a circuit board 10 b according to a second modifiedexample of a preferred embodiment of the present invention will bedescribed with reference to the drawing. FIG. 7 is an explodedperspective view of the circuit board 10 b according to the secondmodified example.

The circuit board 10 b is different from the circuit board 10 in that itpreferably includes external conductors 26 a to 26 d. More specifically,the external conductors 26 a to 26 d are preferably connected to theexternal electrodes 12 a to 12 d, respectively. The via hole conductorsb1 to b4 are preferably connected to the external conductors 26 a to 26d, respectively. With this arrangement, the external electrodes 12 a to12 d are not overlaid on the via hole conductor b1 to b4 when viewed inplan in the z-axis direction. As a result, when a shock is applied tothe printed wiring board 100 from the rearward side towards the forwardside in the z-axis direction, the shock is more effectively preventedfrom being transmitted to the external electrodes 12.

In the following, a circuit board 10 c according to a third modifiedexample of a preferred embodiment of the present invention will bedescribed with reference to the drawings. FIG. 8 is an explodedperspective view of the circuit board 10 c according to the thirdmodified example.

The circuit board 10 c is different from the circuit board 10 in thatinternal conductors 28 a to 28 c are preferably provided in place of theinternal conductors 20 a to 20 f. More specifically, the internalconductor 28 a is preferably provided on the front surface of theinsulating-material layer 16 c and is overlaid on the externalelectrodes 12 a to 12 d when viewed in plan in the z-axis direction.Similarly, the internal conductor 28 b is preferably provided on thefront surface of the insulating-material layer 16 d and is overlaid onthe external electrodes 12 a to 12 d when viewed in plan in the z-axisdirection. The internal conductor 28 c is preferably provided on thefront surface of the insulating-material layer 16 e and is overlaid onthe external electrodes 12 a to 12 d when viewed in plan in the z-axisdirection. Similarly to the circuit board 10, the circuit board 10 chaving the above configuration also prevents the electronic component 50from being detached from the circuit board 10 c.

In the following, a circuit board 10 d according to a fourth modifiedexample of a preferred embodiment of the present invention will bedescribed with reference to the drawings. FIG. 9 is an explodedperspective view of the circuit board 10 d according to the fourthmodified example. FIG. 9 illustrates the insulating-material layers 16 ato 16 e. The insulating-material layers 16 f to 16 h of the circuitboard 10 d are the same or substantially the same as theinsulating-material layers 16 f to 16 h of the circuit board 10illustrated in FIG. 2, and the description thereof will be omitted.

The circuit board 10 d is different from the circuit board 10 in that itis preferably provided with internal conductors 30 a to 30 f and viahole conductors b12 to b17 in place of the internal conductors 20 a to20 f. More specifically, the internal conductors 30 a and 30 b arepreferably provided on the front surface of the insulating-materiallayer 16 c to define a ⅞-turn coil conductor. Further, the internalconductor 30 a is overlaid on the external electrodes 12 a and 12 b whenviewed in plan in the z-axis direction. The internal conductor 30 b isoverlaid on the external electrodes 12 c and 12 d when viewed in plan inthe z-axis direction. The internal conductors 30 c and 30 d arepreferably provided on the front surface of the insulating-materiallayer 16 d to define a ⅞ coil conductor. Further, the internal conductor30 c is overlaid on the external electrodes 12 a and 12 b when viewed inplan in the z-axis direction. The internal conductor 30 d is overlaid onthe external electrodes 12 c and 12 d when viewed in plan in the z-axisdirection. The internal conductors 30 e and 30 f are preferably providedon the front surface of the insulating-material layer 16 e to define a ⅞coil conductor. Further, the internal conductor 30 e is overlaid on theexternal electrodes 12 a and 12 b when viewed in plan in the z-axisdirection. The internal conductor 30 f is overlaid on the externalelectrodes 12 c and 12 d when viewed in plan in the z-axis direction.

Each of the via hole conductors b12 and b13 preferably penetrates theinsulating-material layer 16 c in the z-axis direction to connect endsof the internal conductors 30 a and 30 b to ends of the internalconductors 30 c and 30 d. Similarly, each of the via hole conductors b14and b15 preferably penetrates the insulating-material layer 16 d toconnect ends of the internal conductors 30 c and 30 d to ends of theinternal conductors 30 e and 30 f. Each of the via hole conductors b16and b17 preferably penetrates the insulating-material layer 16 e and areconnected to ends of the internal conductors 30 e and 30 f. In thismanner, the internal conductors 30 a, 30 c, and 30 e and the via holeconductors b12, b14, and b16 define a coil L1. The internal conductors30 b, 30 d, and 30 f and the via hole conductors b13, b15, and b17define a coil L2.

As described above, similarly to the circuit board 10, by using theinternal conductors 30, which define coil conductors, instead of theinternal conductors 20, which define capacitor conductors or groundconductors, detachment of the electronic component 50 from the circuitboard 10 d is effectively prevented. While the internal conductors 30preferably define coil conductors, the internal conductors 30 may besimple wiring conductors which do not define coils.

In the circuit boards 10 and 10 a to 10 d, the external electrodes 14are preferably provided on the bottom surface of the laminated body 11.However, the external electrodes 14 may be provided on a side surface.

In the circuit boards 10 and 10 a to 10 d, the external electrodes 14are not necessarily provided. Specifically, each of the circuit boards10 and 10 a to 10 d may be bonded on a casing instead of being mountedon the printed wiring board 100. In this case, the external electrodes14 are not necessary in the circuit boards 10 and 10 a to 10 d.

Preferred embodiments of the present invention are practicable in acircuit board. In particular, preferred embodiments of the presentinvention are advantageous to effectively prevent an electroniccomponent from being detached from a circuit board.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A circuit board comprising: a laminated body including a laminate ofa plurality of insulating-material layers made of a flexible material, afirst external electrode provided on a top surface of the laminated bodyand on which an electronic component is to be mounted; and a pluralityof internal conductors which, when viewed in plan in a laminationdirection of the laminated body, are overlaid on the first externalelectrode and are not connected to one another through via holeconductors in regions in which the plurality of internal conductors areoverlaid on the first external electrode.
 2. The circuit board accordingto claim 1, wherein the plurality of internal conductors are provided ata top surface side of the laminated body from a central area of thelaminated body in the lamination direction of the laminated body.
 3. Thecircuit board according to claim 1, further comprising: a secondexternal electrode provided on a bottom surface or a side surface of thelaminated body; and a via hole conductor connected to the secondexternal electrode which is not overlaid on the first external electrodewhen viewed in plan in the lamination direction of the laminated body.4. The circuit board according to claim 3, wherein the first externalelectrode is arranged to be connected to the electronic component to bemounted on the top surface; and the second external electrode isarranged to be connected to a wiring board to be mounted on the bottomsurface.
 5. The circuit board according to claim 3, wherein the secondexternal electrode is not overlaid on the first external electrode whenviewed in plan in the lamination direction of the laminated body.
 6. Thecircuit board according to claim 1, wherein a plurality of the firstexternal electrodes are provided and divided into a first group and asecond group; the first external electrodes that belong to the firstgroup are overlaid on a first internal conductor among the plurality ofinternal conductors when viewed in plan in the lamination direction ofthe laminated body; and the first external electrodes that belong to thesecond group are overlaid on a second internal conductor among theplurality of internal conductors when viewed in plan in the laminationdirection of the laminated body, the second internal conductor beingprovided on the same one of the plurality of insulating-material layersas the first internal conductor.
 7. The circuit board according to claim6, further comprising an auxiliary conductor provided on the same one ofthe plurality of insulating-material layers on which the first internalconductor and the second internal conductor are provided, along adirection in which the first internal conductor and the second internalconductor are arranged.
 8. The circuit board according to claim 7,wherein the first internal conductor and the second internal conductorare provided on at least two of the plurality of insulating-materiallayers; and the auxiliary conductor is provided on each of the at leasttwo of the plurality of insulating-material layers on which the firstinternal conductors and the second internal conductors are provided.